On 11/11, Greg Thelen wrote:
>
> The fix is to:
> a) grab rcu lock in sys_ioprio_{set,get}() and
> b) avoid grabbing tasklist_lock.
> Discussion in: http://marc.info/?l=linux-kernel&m=128951324702889
>
> Signed-off-by: Greg Thelen <gthelen@xxxxxxxxxx>
Reviewed-by: Oleg Nesterov <oleg@xxxxxxxxxx>
> ---
> fs/ioprio.c | 13 ++++---------
> 1 files changed, 4 insertions(+), 9 deletions(-)
>
> diff --git a/fs/ioprio.c b/fs/ioprio.c
> index 748cfb9..7da2a06 100644
> --- a/fs/ioprio.c
> +++ b/fs/ioprio.c
> @@ -103,12 +103,7 @@ SYSCALL_DEFINE3(ioprio_set, int, which, int, who, int, ioprio)
> }
>
> ret = -ESRCH;
> - /*
> - * We want IOPRIO_WHO_PGRP/IOPRIO_WHO_USER to be "atomic",
> - * so we can't use rcu_read_lock(). See re-copy of ->ioprio
> - * in copy_process().
> - */
> - read_lock(&tasklist_lock);
> + rcu_read_lock();
> switch (which) {
> case IOPRIO_WHO_PROCESS:
> if (!who)
> @@ -153,7 +148,7 @@ free_uid:
> ret = -EINVAL;
> }
>
> - read_unlock(&tasklist_lock);
> + rcu_read_unlock();
> return ret;
> }
>
> @@ -197,7 +192,7 @@ SYSCALL_DEFINE2(ioprio_get, int, which, int, who)
> int ret = -ESRCH;
> int tmpio;
>
> - read_lock(&tasklist_lock);
> + rcu_read_lock();
> switch (which) {
> case IOPRIO_WHO_PROCESS:
> if (!who)
> @@ -250,6 +245,6 @@ SYSCALL_DEFINE2(ioprio_get, int, which, int, who)
> ret = -EINVAL;
> }
>
> - read_unlock(&tasklist_lock);
> + rcu_read_unlock();
> return ret;
> }
> --
> 1.7.3.1
>
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